How to Plant Onions in Pots

By Jenny Harrington ; Updated September 21, 2017

If you don't have room in the garden to plant onions, consider growing these root vegetables in pots. Onions grow well in large containers where the bulbs have room to develop. The plants need little additional room between the bulbs, so you can grow a decent-sized crop in a small space. Container gardens are not as prone to weeds or soil-born pests, but pot-grown onions do require some additional care if they are to thrive.

Fill a large pot that is at least 12 inches deep and 24 or more inches wide with a sterile potting mixture. Use a soil-less mixture that is rich in organic matter such as peat or compost so that it drains well without drying out.

Mix in a slow-release fertilizer with the soil just prior to planting. Apply a balanced fertilizer at the rate recommended on the label.

Set the pot in an area that receives at least six hours of direct sunlight a day. Morning sun is preferable to afternoon-only sun.

Water the soil from the top of the pot until the excess moisture begins to drain from the bottom. Wait two hours then water in this manner a second time, as this ensures the soil absorbs the maximum amount of moisture prior to planting.

Sow onion seeds 3 inches apart in rows that are also 3 inches apart. Cover the seeds with ¼ inch of potting mixture. Seeds germinate in seven to 10 days.

Water the soil in the pots when the top 1-inch of soil begins to feel dry. Water from the top until the excess moisture begins to drain from the bottom. Pots may need daily watering because they tend to dry out more quickly than garden beds.

Lay a 1- to 2-inch layer of straw mulch over the top of the onions once the leaves are at least 3 inches long. Mulch helps preserve moisture in the pot, but it also protects the tops of the onion bulbs from sunscald.

Harvest the onions when the leaves begin to yellow and fall over. Dump out the container onto a tarp and separate the bulbs from the soil. Add the soil to the compost pile after harvest.

Things You Will Need

Pot

Potting mixture

Fertilizer

Onion seeds

Straw mulch

Tips

There are long-day and short-day onion varieties. Plant long-day if you live in northern areas with more than 12 hours of daylight hours in summer, and plant short-day in southern areas where summer days are shorter.

Plant onions in late spring, about two weeks before the last expected frost.

Warning

Bulb onions, called onion sets, are readily available at garden centers, but they rarely produce full-size bulbs. Use these only if you want to grow green onions.

References

About the Author

Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.